There is growing interest in three-dimensional ultrasonic imaging wherein a three dimensional volume is represented in two dimensions, such as on a video display. One approach to obtaining such images is to use a two-dimensional ("2D") transducer array to obtain three-dimensional image information directly. A 2D array is used to scan electronically in any desired orientation, and thereby acquire the desired information. This approach has considerable problems related to fabrication difficulties, signal to noise difficulties and processing difficulties. Further, it is sometimes desired to obtain a three-dimensional image of a volume which is larger than the scan field of the 2D transducer.
Another approach to three-dimensional imaging is to collect multiple two-dimensional image data frames using a one-dimensional ("1D") transducer array. These frames are subsequently assembled into the desired three-dimensional reconstruction using relative positional information. This approach is also used to scan multiple volumes with a 2D transducer. Multiple three-dimensional data sets are obtained and then subsequently assembled into a larger three-dimensional data set.
As the transducer is manually moved to collect the series of images, translation and rotation of the transducer may impart distortion from one image to the next. While mechanical systems have been developed to control transducer movement and image acquisition, such devices are usually cumbersome to operate and expensive to manufacture. Further, with both manual and mechanical transducer movement, perfectly aligned continuous frames of images are difficult to acquire. There are often gaps in the acquired data which represent gaps between successive frames. When the images are assembled into the three-dimensional volume, these gaps are filled by subsequent processing. To accurately fill these gaps, it is important to know the translation and rotation of the transducer and/or image plane from one image to the next.
Sensors on the transducer have been used to compute rotation and translation of the transducer to correct for the distortion. See for example "MULTIPLE ULTRASOUND IMAGE REGISTRATION SYSTEM, METHOD AND TRANSDUCER", U.S. application Ser. Nos. 08/621,561 (filed Mar. 25, 1996), 08/807,498 (filed Feb. 27, 1997) and 08/916,585 (filed Aug. 22, 1997) to Hossack et al., assigned to the assignee of the present invention and U.S. Pat. No. 5,655,535 to Friemel et al., entitled 3-DIMENSIONAL COMPOUND ULTRASOUND FIELD OF VIEW, all of which are herein incorporated by reference. These references disclose methods of collecting ultrasonic image data and estimating the local displacement of a collection of data points in each image data set Once these local displacements are calculated, the images are then registered and assembled together to generate a 3D volume.